Invincibility:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press Up, Down, Left, Right, Right, Left, Down, Up during the game. The message "Invulnerability On" will appear. Repeat the code to disable. This works in story, endurance, challenge, and multi-player modes.
Unlimited health and turbos:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press Right, Left, Down, Up during the game.

Mega machine guns:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press X, X, Triangle during the game.

One hit kills:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press X, X, Up during the game.

God mode:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press Up, X, Left, Circle during the game. You will have unlimited weapons, health, turbo, and energy.

Weapons for health:
Set the control option to "Classic". Hold L1 + R1 + L2 + R2 and quickly press Triangle, X, Square, Circle during the game.

Alternate weapon view:
Press Select + Right during the game.

Axel:
Go to the Freeway level. It is recommended that you destroy all but one or two of the other vehicles before proceeding. Toward the center of this level is a large construction site with two big cranes. The one on the right is holding a pipe, the one on the left is holding a crate. Use the ridge between the cranes and the road and aim yourself at the control box of the left crane (at the center box). You only need to hit it once with some kind of missile. The crate will then lower into the construction yard. Shoot it open to unlock Axel.

Manslaughter:
Once the ship docks on the island in the Prison Passage level and you can exit the boat, go to the right (left if facing the ship). Follow the waterline until you reach some crates. Shoot them up until a ramp is formed. Shoot the side of the ship until a opening appears. You will unlock Manslaughter there.

Minion:
Unlock all the secret characters, then complete the game in story mode with all of the characters. A FMV sequence showing Minion reassembling and a "Beware of Minion" message will appear. He appears after Sweet Tooth on the character select screen.

Warthog:
Begin the Suburbs level and go to the entrance to the carnival. Turn left and jump off a hill to land on top of a building with a structure on top of it. Blow up the structure to reveal a hole in the building. Fall through the hole and destroy the panel. A message will say Warthog has been unlocked.

Yellow Jacket:
Play the Junkyard level and shoot down the airplane that circles around. A fire missile will do the job, as long as the jet is the only thing in view. The jet will catch on fire, circle, and crash into a wall in the lowest area of the level, that leads to a underground tunnel. The suspended crate's opening faces this area. Follow the tunnel under the sewers, collect the weapons and health, and continue until you see a control panel attached to a large column in the middle of a circular room. Shoot the control panel and a message stating Yellow Jacket has been unlocked will appear. Yellow Jacket will appear inside the destroyed column.

Elevators level:
Start the game on the Highway Loop level. Make sure that there are no more than one or two enemies remaining. Go to the bridge with the gap in it. Go to the side opposite the long tunnel. Facing away from the bridge and to the left on the other side of the wall, you can see two round towers at what seems to be a powerplant. Hit the one closest to the bridge with a gas can. It will pop off and start rolling toward the bridge. Make sure you and none of the enemies are in its path or it will break. It will slowly jump the bridge and will make a hole just inside the tunnel. You will find the cube inside.

Freeway level:
Start an endurance match in the Snowy Roads level. Get ten kills in a row without dying.

Power Plant level:
Head to the end of the Snowy Roads level with the longer building. Face the drop and head to the left side of that gap. Slowly roll over the edge, and there should be a lower level with the cube on it.

Prison Passage level:
Select a pacey car. Do the exact same thing to unlock Warthog (see above), except do not go in the hole in the building. Instead, drive to the end of the row of the buildings going to the left. Then, go to the building opposite that, which has a flat roof. You can do this by driving to the left edge and facing the building. Turbo and jump when you get to the other edge. Make sure to brake when you hit the roof. After this, turn to the building that is next to you and blow up the vent on the roof. You should see the black cube after the vent is destroyed. Turbo and jump when you get to the edge to get the cube and unlock the Prison Passage level.

Prison Ship level:
Get fifteen endurance kills in the Junkyard level to unlock the Prison Ship level in multi-player mode.